JP3198364B2 - Charging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for charging an image forming body by a magnetic brush charging device incorporated in an image forming apparatus such as an electrophotographic copying machine and an electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a corona charger is generally used for charging an image forming body such as a photosensitive drum. This corona charger applies a high voltage to the discharge wire to generate a strong electric field around the discharge wire to perform gas discharge. Done.

The corona charger used in such a conventional electrophotographic image forming apparatus can be charged without mechanically contacting the image forming body, so that the image forming body is damaged during charging. It has the advantage that it does not occur. However, this corona charger has a risk of electric shock or leakage due to the use of high voltage, and ozone generated by gas discharge is harmful to the human body.
It has the disadvantage of shortening the life of the image forming body. Also, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. In addition, noise is generated by the high voltage in the corona charger. This requires a time of 5 seconds or more, which is a major drawback when using an electrophotographic image forming apparatus as a communication terminal or an information processing apparatus.

Many disadvantages of such corona chargers are:
This is because charging is performed mainly by gas discharge.

[0005] Therefore, as a charging device capable of charging an image forming body without performing a high-voltage gas discharge like a corona charger and without causing mechanical damage to the image forming body, a magnet body is used. A charging device that forms a magnetic brush by adsorbing magnetic particles on an enclosed cylindrical carrier, and performs charging by rubbing the surface of the image forming body with a DC bias voltage applied by the magnetic brush. Is JP-A-59-133
No. 569 is disclosed.

Since the magnetic brush is a soft brush made of magnetic particles, the magnetic brush can be charged without damaging the image forming body, and can be used for a fur brush charging device, a charging device using a conductive elastic roll, and the like. It is superior to other contact charging devices. However, even when the magnetic brush charging device was used, uniform charging was not always obtained.

Therefore, for example, Japanese Patent Application Laid-Open No. Hei 4-21873 has proposed a magnetic brush charging method for charging an image forming body by applying an AC bias voltage including a DC component to a magnetic brush. In this publication, charging is performed by setting the AC bias voltage so that the peak-to-peak voltage V _PP exceeds the discharge limit value of the magnetic brush, and the frequency of the AC bias voltage is preferably 100 to 500 Hz. It is said. The magnetic particles used have a particle size of 20 to 200 μm and a resistivity of 10 ⁵ to 10 ⁹
It is described that iron, iron oxide, and ferrite particles of Ω · cm can be provided, whereby uniform charge can be imparted on the image forming body.

[0008]

However, in the charging method described in the above publication, when used for a long time, toner or the like remaining on the photoreceptor adheres to the surface of the magnetic particles forming the magnetic brush, and the resistance of the magnetic brush is reduced. Changes, and the charging performance decreases.In addition, when the environment changes, especially at low temperatures and low humidity, the resistance of the magnetic particles increases, and the magnetic particles adhere to the photoreceptor or charge is not sufficiently injected, causing uneven charging. There is a problem that it occurs.

The present invention solves the above-mentioned problems, and the charging performance does not change even after long-time use and environmental conditions change.
It is an object of the present invention to provide a charging method using a magnetic brush capable of uniform charging at high speed.

[0010]

Means for achieving the above object is to form a magnetic brush made of magnetic particles on a carrier and apply an AC bias voltage having a DC component to the magnetic brush. In the charging method for charging the image forming body by moving and rubbing against the movement of the image forming body, the magnetic particles forming the magnetic brush may be a resin containing conductive fine particles on the surface of the magnetic particle core. Magnetic particles coated with a layer, the ratio of the conductive fine particles to the resin in the resin layer containing the conductive fine particles is 3: 100 to 20: 100, and the average particle size of the conductive fine particles is 1 μm or less. It is a charging method characterized by the following.

Another means for achieving the above object is to form a magnetic brush made of magnetic particles on a carrier, apply an AC bias voltage having a DC component to the magnetic brush, and move the image forming body. In the charging method of charging the image forming member, the magnetic particles forming the magnetic brush are magnetic particles having a surface of a magnetic particle core coated with a resin layer, and The average particle diameter d of the magnetic particles, the thickness h of the resin layer, and the distance D between the carrier and the image forming member are represented by the following relationship: (D × h) / d ≦ 5 μ
m).

Still another means for achieving the above object is to form a magnetic brush composed of magnetic particles on a carrier, apply an AC bias voltage having a DC component to the magnetic brush, and In the charging method of charging the image forming body by moving and rubbing against the movement, the magnetic particles forming the magnetic brush have a concave portion on a surface, and the resin is buried in the concave portion. Charging method, wherein the magnetic particles are magnetic particles.

[0013]

According to the present invention, the surface of the magnetic particles is covered with a conductive or insulating resin having an appropriate layer thickness, or the concave portion is buried with the resin. There is no change in resistance, and there is no contamination of the surface of the magnetic particles by toner or the like.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a copying machine which is an image forming apparatus provided with a magnetic brush charging device to which the present invention is applied, FIG. 2 is an enlarged sectional view showing the magnetic brush charging device of FIG. 1, and FIG.
3 is a graph showing a preferable range of an AC component of a bias voltage applied to the charging sleeve.

In FIG. 1, reference numeral 10 denotes a peripheral speed in the direction indicated by an arrow (clockwise).
A photosensitive drum that is an image forming body that rotates at 240 mm / sec.
This is a negatively chargeable photosensitive drum having an OPC photosensitive layer in which an undercoat layer, a charge generation layer, and a charge transport layer are provided in this order on a conductive base made of aluminum or the like. In the peripheral portion, a magnetic brush charging device 20, a static eliminator 11, an exposure unit 12, on which image light L is incident, a developing unit 30, a transfer roller 13, and a cleaning device
There are 50 etc. The static eliminator 11 includes, for example, an LED array, and is driven under the control of the control unit to erase the charge of the frame portion of the surface of the photosensitive drum 10 outside the incident area of the image light L. In the static eliminator 11, the charge by the magnetic brush charging device 20 has the same polarity as the charge of the toner used in the developing device 30, and the toner is made to adhere to the surface of the photosensitive drum 10 where the image light L is incident. This is unnecessary in the case of reversal development.

Image light L is incident on the charged surface of the photosensitive drum 10 by a slit exposure device or a laser beam scanner to form an electrostatic latent image, and the developing device 30 charges the electrostatic latent image to the photosensitive drum 10. Regular development or reversal development with toner charged to the opposite polarity or the same polarity.

The developing device 30 in the illustrated example forms a magnetic brush made of a two-component developer in which a toner and a magnetic carrier are mixed on a developing sleeve 31 and conveys it in the direction of the arrow.
A bias voltage of the opposite polarity to the charging of the photosensitive drum 10 is applied to 31,
In the case of regular development, it is a magnetic brush developing device that applies and develops to prevent fogging in the case of reversal development and to promote adhesion of toner to an electrostatic image in the case of reversal development. A developer layer is formed in a non-contact manner with the photosensitive drum 10 on the sleeve 31 and is conveyed.
The non-contact development in which the toner 31 flies from the developer layer in the development area near the photoconductor drum 10 and adheres to the electrostatic image may be used.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent from an operation unit (not shown) to a control unit (not shown), the photosensitive drum is controlled by the control unit.
10 starts rotating in the direction of the arrow. As the photoreceptor drum 10 rotates, its peripheral surface is uniformly charged by a magnetic brush charger 20 described later and passes therethrough. An image is written on the photosensitive drum 10 by the exposure unit 12 using the image light L, and an electrostatic latent image corresponding to the image is formed. The electrostatic latent image is developed by the developing device 30, and a toner image is formed on the photosensitive drum 10.

On the other hand, from the paper feed cassette 40, the recording paper P is fed out one by one by a first paper feed roller 41. The fed recording paper P is sent out onto the photosensitive drum 10 by a second paper feed roller 42 that operates in synchronization with the toner image on the photosensitive drum 10. Then, the toner image on the photosensitive drum 10 is transferred onto the recording paper P by the action of the transfer roller 13 to which the bias voltage is applied from the power supply 14, and is separated from the photosensitive drum 10. The recording paper P to which the toner image has been transferred is sent to a fixing device (not shown) via a conveying means 80, is pinched by a heat fixing roller and a pressure roller, is melt-fixed, and is discharged out of the device. Photoreceptor drum 10 that rotates with toner remaining without being transferred to recording paper P
Is scraped off and cleaned by a cleaning device 50 having a blade 51 and the like, and waits for the next recording.

Next, the magnetic brush charging device 20 will be described. In FIG. 2, reference numeral 21 denotes magnetic particles, and 22 denotes magnetic particles made of a non-magnetic and conductive metal such as aluminum.
21 is a charging sleeve which is a carrier, the surface of which has an average surface roughness of 2 to 15 for stable and uniform transport of the magnetic particles 21.
It is preferably set to μm. If the surface is smooth, the transfer cannot be performed sufficiently. If the surface is too rough, an overcurrent flows from the convex portion on the surface, and in any case, uneven charging tends to occur. Sandblasting is preferably used to achieve the above surface roughness. The diameter of the charging sleeve 22 is preferably 5 to 20 mm. With the above diameter, a contact area necessary for charging is secured.
If the contact area is larger than necessary, the charging current becomes excessively large, and if the contact area is small, uneven charging tends to occur. In this embodiment, it is set to 5 mm. Reference numeral 23 denotes a columnar magnet body fixedly disposed inside the charging sleeve 22. The magnet body 23 has an S pole and an N pole so that the surface thereof becomes 700 Gauss on the surface of the charging sleeve 22 as shown in the figure. It has eight magnetic poles alternately magnetized. The charging sleeve 22 is rotatable with respect to the magnet body 23, and is rotated at a peripheral speed of 0.3 to 2.0 times in the same direction as the moving direction of the photosensitive drum 10 at a position facing the photosensitive drum 10. preferable.

Reference numeral 25 denotes a casing which forms a storage portion for the magnetic particles 21. Inside the casing 25, the charging sleeve 22 is provided.
And a magnet body 23 are arranged. A regulating plate 26 is provided at an outlet of the casing 25 to regulate the thickness of the magnetic particle 21 layer adhered to the charging sleeve 22 and carried out. Regulator 26
The gap Dh between the tip of the magnetic sleeve 21 and the charging sleeve 22 is determined by the amount of the magnetic particles 21 conveyed, that is, the amount of the magnetic particles 21 on the charging sleeve 22 in the charging area is 10 to 300 mg / cm ^2, particularly preferably 30 to 1
Adjusted to be 50 mg / cm ² . 27 is a stirrer for stirring the magnetic particles 21 to make them uniform.

The gap Dsd between the charging sleeve 22 and the photosensitive drum 10 can be set in the range of 0.1 to 5 mm. If the gap Dsd is smaller than this range, the durability of the photosensitive drum 10 and the like is quickly reduced. Or it becomes difficult to form the magnetic brush 21A composed of the magnetic particles 21 that appropriately rubs the photoconductor drum 10, and conversely, if the magnetic brush 21A becomes wide, the magnetic brush 21A makes uniform contact with the photoconductor drum 10. Therefore, it becomes difficult to uniformly charge the photosensitive drum 10. In this embodiment, Dh = Dsd. Thereby, the gap Dsd between the charging sleeve 22 and the photosensitive drum 10 is connected by the conductive magnetic brush 21A whose thickness is regulated.

The bias voltage applied to the charging sleeve 22 is an AC bias voltage in which an AC component is superimposed on a DC component, and the DC component is suitably in the range of -500 to -1000 V which is equal to the charging voltage of the photosensitive drum 10. However, it is preferable that the AC component be within the white area shown in FIG. 3 from the viewpoint of stable charging. In FIG. 3, the shaded area in the vertical line indicates a range in which dielectric breakdown is likely to occur, the shaded area indicates a range in which charging unevenness is likely to occur, and the low-frequency area in which scattered shades are applied.
This is a range where charging unevenness occurs due to a low frequency. The waveform of the AC component is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or the like. In this embodiment, the AC bias voltage of the DC component was -700 V, the AC component V _PP was 1,000 V, and the frequency was 1.5 kHz.

The photosensitive drum 10 comprises a conductive base 10b and a photosensitive layer 10a covering the surface thereof, and the conductive base 10b is grounded.

Reference numeral 24 denotes a bias power supply for applying the AC bias voltage between the charging sleeve 22 and the conductive substrate 10b. The AC bias voltage is applied to the charging sleeve 22 through a protection resistor R.
Has been applied. The bias power supply 24 performs constant voltage control for the DC component and constant current control for the AC component.

The magnet body 23 has N and S magnetic poles at equally spaced positions in the circumferential direction and rotates in the direction opposite to the direction in which the magnetic particles 21 are conveyed. It may be stationary or may rotate in the opposite direction to the magnet 23. Further, the above-described rotation direction of the charging sleeve 22 and the magnet body 23 may be such that the transport direction of the magnetic brush 21A at the position where the charging sleeve 22 faces the photosensitive drum 10 is opposite to the moving direction of the photosensitive drum 10. Good. However, the uniformity of charging of the photosensitive drum 10 and the reducibility of the magnetic brush 21A into the container 25 after passing through the rubbing position of the photosensitive drum 10
In terms of durability, etc., the above-described transport direction of the magnetic brush is the same as the moving direction of the photosensitive drum 10, and the transport speed is 0.3 to 2.0 times the moving speed of the photosensitive drum 10. Is preferred. In this embodiment, the moving speed of the photosensitive drum 10 and the moving speed of the charging sleeve 22 are the same in the same direction in the facing portion. When the charging sleeve 22 is rotated at the same speed as the peripheral speed of the photoconductor drum 10 in the same direction as the arrow while rotating the photoconductor drum 10 in the direction indicated by the arrow, the layer of the magnetic particles 21 adhered and conveyed to the charging sleeve 22 is formed. The thickness of the magnetic particles 21 is regulated by the regulating plate 26, and the magnetic particles 21
A magnetic brush 21A is formed by magnetically connecting the photosensitive drum 10 at a position facing the photosensitive drum 10 on a chain 22 to form a kind of brush.
Is formed. Then, the magnetic brush 21A is conveyed in the rotation direction of the charging sleeve 22, and the photosensitive layer of the photosensitive drum 10 is
Touch 10a. Since the AC bias voltage is applied between the charging sleeve 22 and the photoconductor drum 10, charges are injected onto the photoconductor layer 10a via the magnetic brush 21A to perform uniform high-speed charging.

Next, the magnetic particles used in the present invention will be described.

In general, the magnetic particles used in the magnetic brush charging device include iron, chromium, nickel, and the like as the magnetic particles of the conventional magnetic carrier particles of a two-component developer.
Ferromagnetic particles such as metals such as cobalt, or compounds or alloys thereof, such as ferric oxide, γ-ferric oxide, chromium dioxide, manganese oxide, ferrite, and manganese-copper alloy are used. .

The magnetic particles as described above are preferably spherical. This also has the effect that the particle layer formed on the carrier is made uniform and a high bias voltage can be applied uniformly to the carrier. That is,
The fact that the magnetic particles are spherical is (1) In general, the magnetic particles are easily magnetized and adsorbed in the long axis direction, but the spherical particles lose their directionality, so that the layer is formed uniformly and locally. (2) With the increase in the resistance of the magnetic particles, the edge portion as seen in the conventional particles is eliminated, and the concentration of the electric field on the edge portion does not occur. As a result, even when a high bias voltage is applied to the magnetic particle carrier, an effect is obtained in that the surface of the image forming body is uniformly discharged and uneven charging does not occur.

The spherical particles exhibiting the above effects have a resistivity of the magnetic particles of 10 ³ Ω · cm or more and 10 ¹² Ω · cm or less, particularly 10 ⁶ Ω · cm or less.
It is preferable that conductive magnetic particles are formed so as to be Ω · cm or more and 10 ¹⁰ Ω · cm or less. This resistivity makes the particles 0.50
After tapping in a container having a sectional area of cm ^2,
A value obtained by applying a load of 1 kg / cm ² on the packed particles and reading a current value when a voltage that generates an electric field of 1,000 V / cm between the load and the bottom electrode is applied. If the resistivity is low, when a bias voltage is applied to the carrier, electric charges are injected into the magnetic particles, so that the magnetic particles tend to adhere to the surface of the image forming body, or dielectric breakdown of the image forming body due to the bias voltage is prevented. It is easy to happen. On the other hand, if the resistivity is high, charge injection is not performed and charging is not performed.

Next, the magnetic particles used in the present invention will be described.

(Example 1) The magnetic particles used in the first aspect of the present invention use the above-mentioned magnetic particles as a magnetic particle core, and the surface thereof has an average particle size of, for example, conductive titanium oxide, iron, nickel, or cobalt. 1 μm or less, resistivity 10 ⁴ Ω · cm
Styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester containing the following conductive fine particles dispersed at a weight ratio of 3/100 to 20/100 With resin such as resin,
Magnetic particles 21a shown in FIG. 4 are obtained by subjecting the particles obtained by coating to a thickness of 0.5 to 5 μm, preferably 1 to 2 μm, with a conventionally known average particle size sorting means. In the figure, reference numeral 211 denotes a magnetic particle core, 212 denotes a resin layer covering the surface of the magnetic particle core 211, and 213 denotes conductive fine particles. Magnetic particles 2
The average particle size (weight average) of 1a is 30 to 100 μm, its saturation magnetization is 20 to 100 emu / g, and the resistivity of the magnetic particles is 10 ² to 10 ¹⁰ Ω · c.
m, the average particle diameter (weight average) is preferably 40 to 70 μm, the saturation magnetization thereof is 40 to 80 emu / g, and the resistivity of the magnetic particles is preferably 10 ⁷ Ω · cm or less.

The reason for the above is that if the ratio of the conductive fine particles / coating resin is less than 3/100, the resistance of the magnetic particles 21a increases, causing uneven charging and adhesion of the magnetic particles. On the other hand, if the ratio of conductive fine particles / coated resin exceeds 20/100, the ratio of conductive fine particles 213 exposed on the surface of magnetic particles 21a increases, resulting in the same properties as magnetic particles not coated with resin, resulting in charging due to environmental conditions. Uneven charging and magnetic particle adhesion occur during fluctuations and low temperature and low humidity. Furthermore, when the average particle size of the conductive fine particles 213 exceeds 1 μm, a part of the conductive fine particles 213 protrudes from the surface of the resin layer 212 to be coated, and the lines of electric force concentrate on this portion, so that electric discharge easily occurs and fine particles are formed. This is because ring mark-shaped uneven charging occurs.

(Actual Photo Test 1) A magnetic particle core 211 having a spherical ferrite having an average particle diameter of 60 μm and a saturation magnetization of 70 emu / g, and a conductive titanium oxide having several particle diameters as conductive fine particles 213. Various kinds of magnetic particles 21a were experimentally produced, and a magnetic brush charging device 20 using the magnetic particles 21a was sequentially installed in the copying machine, and an image forming test was performed. In the test, the image forming apparatus was allowed to stand overnight in a high-temperature and high-humidity atmosphere of 30 ° C. and RH of 80%. A real-life test was performed in a low-temperature and low-humidity atmosphere of 20% (this is referred to as LL). Charging unevenness (image density unevenness), magnetic particle adhesion (image defect based on magnetic particle adhesion, carrier adhesion in Table 1) Image defects) were measured.

The measurement of the charging unevenness is performed by measuring the density of the high-density solid image portion with an image analyzer RT-2000 (manufactured by Yarman).
The 100 μm × 100 μm square portion of the sample was measured at 100 points (100 data points) using
The results were evaluated according to the “x” method, and the obtained results are shown in Table 1.

Evaluation standard of charging unevenness “○”: when the average density of 100 data items is 1.3 or more and the standard deviation of 100 data items is 0.2 or less “△”: average of 100 data items When the concentration is 1.2 or more and less than 1.3 and the standard deviation of 100 data items is 0.2 or less `` × '' ... When the average concentration of 100 data items is less than 1.2 or the standard deviation exceeds 0.2 Magnetic particles Image defects due to adhesion are measured by measuring the occurrence of fog on the white background with an optical densitometer, and "○" ... when the fog on the white background is 0.01 or less "x" ... In the case of exceeding, use a modified machine of Konica 4045 copier with built-in magnetic brush charging device loaded with magnetic particles 21a which obtained good results in the above test, and increased the line speed to 400 mm / sec. As a result of the actual shooting test, Clear image was obtained in (○ mark in the column after 10,000 C in Table 1).

[0038]

[Table 1]

The coverage in Table 1 represents the weight ratio of the coating layer to the weight of the whole magnetic particles in%.

(Embodiment 2) Next, the magnetic particles used in the second aspect of the present invention will be described.

The magnetic particles use the magnetic particle core 211 of Example 1 as the magnetic particle core, and the surface thereof is made of, for example, a styrene resin, a vinyl resin, an ethylene resin, a rosin modified resin, an acrylic resin, a polyamide resin, or the like. The particles are obtained by coating particles obtained by coating with a resin such as an epoxy resin or a polyester resin to a thickness described later by a conventionally known average particle size selecting means. The average particle size (weight average) is 30 to 100 μm, the saturation magnetization is 20 to 100 emu / g, the resistivity of the magnetic particles is 10 ² to 10 ¹⁰ Ω · cm, the average particle size (weight average) is 40 to 70 μm, The saturation magnetization is preferably 40 to 80 emu / g, and the resistivity of the magnetic particles is preferably 10 ⁷ Ω · cm or less.

The magnetic particles are magnetic particles as shown in FIG.
21b, the magnetic particle 21b is a magnetic particle 21b in which the surface of the magnetic particle core 211 is covered with a resin layer 212, and the average particle diameter d of the magnetic particle 21b, the film thickness h of the resin layer 212, the charging sleeve 22, and the photosensitive drum 10. (Dsd in claim 2) satisfies the following relationship (Dsd × h) / d ≦ 5 (both Dsd, h, and d are in μm).

That is, the charging sleeve 22 and the photosensitive drum
The sum of the thickness of the resin layer 212 existing in the gap between 10 and 10 μm
It is as follows. If the above value exceeds 10, a thick insulating layer exists between the charging sleeve 22 and the photoconductor drum 10, so that the charge injection into the photoconductor becomes insufficient, causing uneven charging and the photoconductor drum. Adhesion of magnetic particles to 10 occurs. The adhesion of the magnetic particles is caused when the photoconductor becomes insufficiently charged and a potential difference is generated between the charging sleeve 22 and the surface of the photoconductor drum 10, and the magnetic particles are reversely developed on the surface of the photoconductor by the electric field caused by the electric field.

(Actual Test 2) Three types of spherical ferrites having an average particle size d of 60 μm, 80 μm, and 120 μm are used as the magnetic particle core 211, and the thickness h of the resin layer 212 and the Ds
Several kinds of magnetic particles 21b were prototyped by changing d as shown in Table 2.
An image forming test was conducted by incorporating the magnetic brush charging device 20 using the magnetic particles 21b sequentially into the copying machine. In the test, the image forming apparatus was allowed to stand overnight at a high humidity of 30 ° C. and a relative humidity of 80%, and then subjected to a normal atmosphere of 20 ° C. and a relative humidity of 50% (N.N.
) And under a low temperature and low humidity atmosphere of 10 ° C and 20% (this is referred to as L.
L.), and image defects such as charging unevenness (image density unevenness) and adhesion of magnetic particles (image defect based on adhesion of magnetic particles) were measured. Judgment standard is live-action test 1
Is the same as

As shown in Table 2, the results of this test are as follows:
When the value of (Dsd × h) / d was 5 or less, good results were obtained, but those exceeding 5 were poor and not suitable for practical use.

A Konica 4045 copier modified with a magnetic brush charging device loaded with magnetic particles 21b having good results obtained in the above test and having a line speed increased to 400 mm / sec was used for 10,000 each. As a result of performing the actual shooting test each time, clear images with high resolution and high density were obtained in all cases (indicated by a circle in the column after 10,000 C in Table 1).

[0047]

[Table 2]

(Example 3) Further, magnetic particles used in the third aspect of the present invention will be described.

The magnetic particles are formed by burying a resin in a magnetic particle core having a concave portion on the surface, and irregular magnetic particles such as ferrite or iron having a concave portion are used for the magnetic particle core.

FIG. 6 is a schematic view of the magnetic particles. In the figure, 21c is a magnetic particle of the present invention, 215 is a magnetic particle core, and 216 is a resin to be buried. In order to obtain the magnetic particles 21c, a powder obtained by sufficiently making the magnetic particle core 215 and the resin 216 mixed and stirred at a predetermined ratio is applied to the surface of the magnetic particle core 215 and the concave portions of the resin 216 powder. When the two are sufficiently mixed, most of the powder of the resin 216 becomes the magnetic particle core 2
Buried in the fifteen recesses, one that hardly adheres to the surface is obtained. After this state, the magnetic particle core 21
When 5 is heated to melt the resin 216 powder, magnetic particles 21c shown in FIG. 6 are obtained.

The resin 216 to be buried is polystyrene,
Styrene acrylic resin, acrylic resin, epoxy resin,
Fluororesin, polyester resin, and the like are used, but are not limited thereto. The amount of the resin 216 used is 0.1 to 10 parts by weight, preferably 0.4 to 100 parts by weight based on the weight of the magnetic particle core 215.
To 5.0 parts by weight.

The magnetic particles 21c thus obtained are:
The amount of the resin 216 attached is 0.1 to 10% by weight, and the saturation magnetization is 20 to 100 e.
mu / g, average particle size is 30 to 100 μm, resistivity is 10 ¹⁰ Ω · cm or less, and apparent density is 2.0 to 3.0 g / cm ³ , but adhesion amount of resin 216 is 0.4 to 5.0% by weight , Saturation magnetization 40-80e
mu / g, average particle size 40～70Myuemu, is preferably less resistivity of 10 ⁷ Ω · cm.

(Actual Photo Test 3) Amorphous iron powder and spherical iron powder having no concave portions on the surface were used as the magnetic particle cores 213. A similar test was performed. As shown in Table 3, good results were obtained using amorphous iron powder with a coverage of 2 to 3%, but a coverage of 0.5% was obtained using spherical iron powder.
The following resin 216 is easily peeled, and the characteristics as magnetic particles become unstable, and the peeled resin 216 (generally referred to as white powder) adheres to the photoreceptor and exerts an adverse effect, or is mixed into a developing device to remove the developer. There was a defect that the chargeability was changed. In this test, a good copy test was performed 10,000 times in the same manner as in the actual test 1, but the result was good and proved to be suitable for practical use. The determination conditions and the display method of the actual shooting test are exactly the same as those of the actual shooting test 1.

[0054]

[Table 3]

[0055]

According to the charging method of the present invention, the resistivity of the magnetic particles and the resistance of the magnetic brush do not change even after long-time use or environmental conditions change. And prevent fluctuations in charging performance when environmental conditions change,
It is possible to provide a charging method using a magnetic brush capable of performing high-speed and uniform charging without causing adhesion of magnetic particles to a photoreceptor and uneven charging even at low temperature and low humidity.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an image forming apparatus provided with a charging device to which the present invention is applied.

FIG. 2 is an enlarged sectional view showing one embodiment of a magnetic brush charging device to which the present invention is applied.

FIG. 3 is a graph showing a preferable range of an AC component of a bias voltage applied to a charging sleeve.

FIG. 4 is a schematic diagram showing magnetic particles of Example 1 of the present invention.

FIG. 5 is a schematic diagram showing magnetic particles of Example 2 of the present invention.

FIG. 6 is a schematic diagram showing magnetic particles of Example 3 of the present invention.

[Explanation of symbols]

 10 Photoconductor drum (image forming body) 20 Magnetic brush charger 21, 21a, 21b, 21c Magnetic particles 21A Magnetic brush 22 Charging sleeve (carrier) 23 Magnet body 24 Bias power supply 26 Regulator plate R Protection resistor

Continued on the front page (72) Inventor Shizuo Morita 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Inventor Hiroyuki Nomori 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation Examiner, Yaichi Inoue (56) References JP-A-4-21873 (JP, A) JP-A-59-133569 (JP, A) JP-A-63-135956 (JP, A) JP-A-63-187267 (JP, A) Kaihei 4-234063 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/02 G03G 15/02-15/02 103 G03G 15/09-15/095 G03G 9 / 10-9/113

Claims (3)

(57) [Claims] A magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush to move the magnetic brush with respect to the movement of the image forming body.
In the charging method of charging the image forming body by rubbing, the magnetic particles forming the magnetic brush are magnetic particles having a surface of a magnetic particle core coated with a resin layer containing conductive fine particles. A charging method, wherein the ratio of the conductive fine particles to the resin in the resin layer containing the conductive fine particles is 3: 100 to 20: 100, and the average particle diameter of the conductive fine particles is 1 μm or less. 2. A magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush to move the magnetic brush with respect to the movement of the image forming body.
In the charging method of charging the image forming body by rubbing, the magnetic particles forming the magnetic brush are magnetic particles in which the surface of a magnetic particle core is coated with a resin layer, and The average particle diameter d, the thickness h of the resin layer, and the distance D between the carrier and the image forming body are represented by the following relationship: (D × h) / d ≦ 5
m) A charging method characterized by satisfying the following. 3. A magnetic brush made of magnetic particles is formed on a carrier, and an AC bias voltage having a DC component is applied to the magnetic brush to move the magnetic brush with respect to the movement of the image forming body.
In the charging method for charging the image forming body by rubbing, the magnetic particles forming the magnetic brush have a concave portion on a surface, and the concave portion is a magnetic particle embedded with a resin. A charging method comprising: